Rentention of urine in the bladder is a serious problem in paraplegic and quadraplegic mammals, such as dogs and humans. It results from a failure to empty the bladder due to an interruption of the spinal pathway from the pontine micturition center in the brain to the bladder. Eventually such a condition will induce urinary tract infection and renal complications that often lead to, or cause, premature death. Prior attempts have been made to induce micturition in humans, and in test mammalian animals by electrical stimulation of pre- and post-ganglionic parasympathetic neurons that innervate the bladder. In such prior experimental attempts, the electrical stimulator has been connected directly to, or wrapped around, the nerves that are to be stimulated.
Neurophysiologically, if a specific nerve is to be electrically stimulated, it must be isolated from other excitable tissues. In a traditional experimental method, a pair of stimulating electrodes are directly attached to each nerve root to be stimulated, sometimes with use of an associated isolating protective or insulating device. However, because there is only limited space available in the sacral canal of test mammals, and also of humans, and further because of the difficulty in locating a specific nerve root, it has been observed that prior attempts to arrange electrodes to be operatively associated with only one or two nerve roots functions to restrict stimulation to only a portion of the motor innervations of the bladder of a mammalian test animal.
Heretofore, it was thought to be desirable that the first sacral roots be spared from stimulation to avoid a stimulation that would produce unnecessary movements of the body and the legs. While such thought probably had stimulus in the fact that experimenters were working only with test animals and sought to eliminate unnecessary body and muscle movement of the test animal, the stimulation and movement of muscles is probably desirable to limit deterioration of the musculature, particularly in a human. The first sacral roots may contain motor fibers both to the detrusor muscle, and to other muscles in both animals and humans. In so far as stimulation of the first sacral roots may effect stimulation that causes body and muscle movement in a human, such stimulation is not necessarily to be avoided.
However, prior art methods for stimulating a mammalian animal's bladder to effect discharge therefrom, has employed restricted stimulation in attempts to isolate the electrical stimulation to a particular nerve root, and to avoid spreading the stimulating electricity to other excitable tissues.
Reports of: (a) Agnew, W. F., et al., The Effects of Electrical Stimulation On The Central And Peripheral Nervous Systems, NIH Contract, NO-1-NS-0-2275 Quarterly Progress Report, Oct. 1-15, (1979); (b) Brindley, G. S., An Implant To Empty The Bladder Or Close The Urethra, J. Neurol. Neurosurg. Psychiat., 40: 358-369, (1977); (c) Schmidt, R. A., et al., Feasibility of Inducing Micturition Through Chronic Stimulation Of Sacral Roots, Urology, 12: 471-477, (1978); (d) Tanagho, E. A., et al., Studies On The Feasibility of Urinary Bladder Evacuation By Direct Spinal Cord Stimulation, NIH Contract, NO-1-NS-3-2307, Quarterly Progress Report, Apr. 1-14, (1981); all advise that prior investigations have attempted to stimulate motor neurons of the bladder by placing stimulating electrodes as close as possible to the specific nerve to be stimulated, often accompanied by the presence of some insulating device. However, it has been observed that tightly attached electrodes and protective devices obstruct axonal transport, cause leakage of the cerebrospinal fluid, and may irreparably damage the animal's nerve roots.
Brindley, G. S., An Implant To Empty The Bladder Or Close The Urethra, J. Neuro. Neurosurgical Psychiatry, 40: 358-369, (1977), designed an implant to stimulate only separate strands of sacral roots in the sacral canal. However, leakage of cerebrospinal fluid, as well as injury to the spinal roots is reported to have occurred with said apparatus.
The general concept of using only intermittent stimulation to induce animal micturition has been previously suggested by others. U. Jonas, and E. A. Tanagho, as reflected in their reports, Studies On The Feasibility Of Urinary Bladder Evacuation By Direct Spinal Cord Stimulation, and, Poststimulus Voiding: A Way To Overcome Outflow Resistance, Investigative Urology, 13: 151-153, (1975), intermittently stimulated the sacral roots to achieve micturition. However, they achieved micturition only when a four-channel urethral catheter was positioned in the bladder.
Stimulating currents which are non-injurious to the body have been previously explored and reported. P. C. Tang, pH Changes Induced By Electrical Stimulation, Physiologist, 22: 122, (1979). It has been observed that monophasic electrical pulses, which are essentially intermittent direct currents, generate gases and cause severe pH changes at the electrode terminals. Alternating currents, such as capacitor-coupled and bi-phasic pulses are generally injurious to the body. The voltage of capacitor-coupled pulses varies with the frequency of the stimulation, while the bi-phasic pulses are difficult to balance and expensive to use.